Krell Solo 375 Mono-Block Amplifier Reviewed

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Krell Solo 375 Mono-Block Amplifier Reviewed

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I've never been a Diana Krall fan, but it's hard not to be captivated by Wallflower, her new album of covers of classic rock tunes. In just the first 20 or 30 bars of her take on Elton John's "Sorry Seems to Be the Hardest Word," I learned a lot about the Solo 375. I was struck by how intimate and warm Krall's voice sounded. She sounded like she was right in the room with me, about eight feet away, with very little ambience. In fact, based on her voice, I'd almost have thought someone deadened up my listening room with about 30 square feet of Sonex foam. But the instruments sounded huge and spacious, much as in Elton John's original recording. The spaciousness didn't sound like the result of exaggerated treble or phasiness, and it rarely produced a "wow" reaction from me; it merely sounded natural. In terms of sheer involvement, this was a higher level than what I'm used to hearing from my Revels.

You're probably sick of hearing the Mark Ronson/Bruno Mars tune "Uptown Funk," but it happened to come up on the home page of the Tidal app, so I played it just out of curiosity. It'd be easy to dismiss this as insubstantial pop fluff; but, through the Solo 375 and the Resolution 1 speakers, I could hear that it's actually a musical and sophisticated production. The Solo 375's sound suited Bruno Mars' voice, which is smooth but not deep and thus might sound grating through some amps. Through the Solo 375, it sounded positively liquid, yet there was nothing soft about the bottom end; the Solo 375 kept each Resolution 1's dual woofers in perfect control, producing tight, deep, powerful bass tones. Again, the unexaggerated, natural-sounding spaciousness pulled me in.�

Based on these and some cuts I'd heard before, I was starting to wonder if the Solo 375/Resolution 1 combo could conjure a really huge sense of space. I found out fast when, on its own, Tidal went straight into Mars' "Locked Out of Heaven." The tune's background vocals almost literally jumped out of the speakers, actually seeming to come from behind me. This is a pretty easy trick for big panel speakers like MartinLogans and Magnepans, but not many systems using conventional dynamic drivers can so convincingly wrap sound around you.

Having heard enough pop singers for a while, I shifted over to one our greatest anti-pop singers: James "Blood" Ulmer. Ulmer's Odyssey album is an idiosyncratic masterpiece, consisting only of drums, violin (often played through a wah-wah pedal), hollowbody electric guitar (with all the strings tuned to A), and Ulmer's inimitable vocal stylings. The Solo 375 got all the spacing right, the natural reverb of the space in which the drums were recorded contrasting perfectly with the much more intimate sound of the close-miked vocals and the reverb-soaked violin lines. Ulmer's vocals also sounded just right: smooth and soulful, but with that little trace of edge that makes Blood Blood. (BTW, I've seen Ulmer live more than any other artist, in widely varying venues and numerous musical settings, so I'm pretty familiar with his sound by now.)

Not surprisingly, the Solo 375 sounded great with rock, too. R.E.M.'s "Pilgrimage," from Murmur, the group's first full-length album, isn't something anyone would mistake for a Led Zeppelin or Deep Purple tune, but all the elements are there: a dynamic, insistent drum sound with a huge-sounding snare and a powerful vocal performance backed by highly reverberant background vocals. (OK, so it has chimes�in unison with the guitar. That doesn't mean it's not rock.) The spaciousness that worked so well for the other recordings came through on "Pilgrimage," too, and I especially loved the power of Bill Berry's kick drum and the way his firm snaps of the snare drum came through with loads of dynamics but not a track of edge.

Basically, the Solo 375 sounded like the world's most powerful tube amp. The tonal and spatial character, combined with the warmth of the mids, reminded me of some of the big push-pull tube amps with quartets or octets of KT88 tubes. By and large, that's a good thing.

The Downside
One of the things that made the Solo 375 remind me of a tube amp is that the top end is smooth and not in any way "hifi sounding." Personally, I like that. But I know some audiophiles don't--they want to hear every last little detail in a recording, even if they need a somewhat elevated or edgy treble to get it. If that's you, that's okay. In audio, you gotta go with what makes you happy. Just know that, if what makes you happy is a lot of treble detail (apparent or actual), the Solo 375 probably isn't your amp.

Comparison and Competition
I had a chance to compare the Solo 375 with a couple of other big solid-state amps: Class� Audio's $7,000 CA-2300 and Pass Labs' $11,500 X350.5. The latter, incidentally, runs in Class A for the first 40 watts; so, for all intents and purposes, it's almost always running in Class A and thus makes an interesting comparison for the Solo 375. Using a one-kilohertz test tone, I matched the amps' output levels within �0.1 dB and connected them all to the Resolution 1 speakers.

A particularly illuminating track for comparing almost any kind of audio gear is Trilok Gurtu's "Once I Wished a Tree Upside Down," a light saxophone melody backed by shakers, tabla, and synthesizers. In the intro, the shakers swirl around your listening room; the degree to which they wrap around my listening chair is one way I judge a system's soundstaging capability. With the CA-2300, the treble sounded wonderfully detailed and delicate, but the action all seemed to be taking place in front of me rather than around me. With the X350.5, I got a greater sense of spaciousness and wraparound, but the treble didn't sound as smooth as with the Class� or the Krell. The Krell got the spaciousness just right, but because its treble was smoother/softer, it didn't have that level of excitement that the others did.�

I listened to some more jazz and pop cuts through all three amps, but the comments were the same thing over and over. All three had ample dynamics and bass; it's mostly the character of the treble and the spaciousness of the sound that varied. Which one will you like better? That depends on your personal taste. But if smoothness and spaciousness rank high on your list of priorities, the Krell seems like the best bet to me.

Spending $17,500 on a pair of mono-block amps is a lot, but the Solo 375 delivers a lot. It combines a very smooth, un-solid-state, un-hifi sound with loads of power and dynamics, plus a design that works great whether you're plopping the amps on the floor by the speakers or shoving them out of sight into a closet or equipment cabinet. In fact, I'd go so far as to say I've never encountered another amp that combines the Solo's 375 warm, wonderful, involving sound with such a practical and versatile design.

Additional Resources
� Visit our Stereo, Mono and Audiophile Amplifiers category page for similar reviews.
Krell Foundation AV Preamp Reviewed at
Krell Announces the Digital Vanguard Integrated Amplifier at

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